1. Technical Field
The invention relates to photonic devices. In particular, the invention relates to photonic detectors that employ surface plasmons.
2. Description of Related Art
Photonic detectors or sensors of various types, employed either singly or in an array, are used in a wide variety of modern optical and infrared (IR) imaging systems. For example, modern digital photography depends almost exclusively on photonic sensor arrays that employ either charge-coupled devices (CCDs) or complementary metal oxide semiconductor (CMOS) active pixel sensors for capturing and creating digital images. Other photonic detection technologies are also often employed, especially in multispectral and hyperspectral imaging systems having operational imaging requirements that may extend well into the long-wave IR (LWIR) spectral range. These other photonic detection technologies include, but are not limited to, photovoltaic devices (e.g., p-i-n photodiodes), devices that utilize photoconduction (e.g., phototransistors), and sensors based on the pyroelectric effect or a temperature-dependent change in resistivity (e.g., bolometers or microbolometers). For example, current state-of-the-art IR focal plane photonic sensor arrays typically employ either mercury cadmium telluride (HgCdTe) IR photodetectors or gallium arsenide (GaAs) quantum well IR photodetectors (QWIPs).
Unfortunately, the existing photonic detectors often fail to meet one or more objectives of many modern imaging systems that cover the visible to LWIR spectrum. For example, semiconductor-based HgCdTe and GaAs QWIP based IR photonic detectors typically must be operated at relatively low temperatures (e.g., below 77° K.) to achieve an acceptable level of performance. As such, IR imaging systems that employ these semiconductor-based IR photonic detectors are not typically able to be used when room-temperature operation is desired unless an associated cost, complexity and power consumption for sensor cooling can be accommodated. In addition, many imaging systems based on semiconductor photodiodes are limited to a finite number of spectral bands due to the material bandgaps used in such devices. On the other hand, imaging systems based on bolometers (e.g., microbolometer arrays) may be operated at room temperature. However, microbolometer arrays generally exhibit spectral sensitivity that is limited to the LWIR spectrum which may preclude their use in some multi-spectral imaging applications. Furthermore, in general the above-discussed photonic detectors typically lack an integrated ability to achieve wavelength tunability. Instead, imaging systems that employ these technologies typically rely on techniques such as beam splitting and filtering in front of the photonic detector array to provide wavelength agility (e.g., dynamic spectral tunability) required for some multispectral and hyperspectral applications.
As such, there is considerable interest in providing a means for photonic detection that will facilitate implementation of high resolution, multispectral imaging systems. In particular, there is need for a photonic detection means that one or more of provides high optical sensitivity at relatively higher temperatures (e.g., room temperature), facilitates implementation of sub-wavelength pixels and provides for both spectral discrimination and dynamic spectral tunability. Providing such means would satisfy a long felt need.